A solenoid device in which a plunger is made to reciprocate by using an electromagnetic coil is conventionally known as a part used for a relay or the like (refer to the following patent literatures 1 to 3). FIGS. 28 and 29 illustrate an example of a conventional solenoid device.
A conventional solenoid device 9 has two electromagnetic coils 91 each obtained by winding a conductive wire in a cylindrical shape, a yoke 92 made of soft magnetic material, and two plungers 93. Each of the plungers 93 has a core part 93a made of soft magnetic material and a contact part 93b made of insulating member. The core part 93a is disposed in the center of the electromagnetic coil 91. The yoke 92 is constructed by combining a plurality of magnetic members. In the center of the electrometric coil 91, an in-coil yoke 92a as a part of the yoke 92 is provided.
As illustrated in FIG. 29, when current is passed to the electromagnetic coil 91, a magnetic flux Φ is generated. The magnetic flux Φ flows in the core part 93a of the plunger 93 and the yoke 92. Consequently, the core part 93a is magnetized and attracted by the in-coil yoke 92a. A spring member 97 is provided between the core part 93a and the in-coil yoke 92a. As illustrated in FIG. 28, when the current to the electromagnetic coil 91 is stopped, the magnetic flux Φ vanishes. By the pressing force of the spring member 97, the core part 93a moves apart from the in-coil yoke 92a. 
The solenoid device 9 is used for a relay 90. The relay 90 has two contact parts 96. Each of the contact parts 96 has a moving-contact supporting part 94 supporting a moving contact 940 and a fixed-contact supporting part 95 supporting a fixed contact 950. As illustrated in FIGS. 28 and 29, by making the plunger 93 reciprocate in the axial directions (Z directions) of the electromagnetic coil 91, the contact part 93b of the plunger 93 is made contact with the moving-contact supporting part 94, and the moving contact 940 and the fixed contact 950 come into contact with each other and are moved apart from each other. In such a manner, the relay 90 is turned on/off.
In the conventional solenoid device 9, however, one plunger 93 is made to reciprocate by using one electromagnetic coil 91. Consequently, in the case of making the plurality of contacts 96 come into contact and moved apart, the electromagnetic coils 91 of the number corresponding to the number of contacts 96 are required. There is a problem that the number of the electromagnetic coils 91 easily increases. Since the electromagnetic coil 91 is relatively expensive, when the number of electromagnetic coils 91 increases, the size increases, and the manufacture cost of the solenoid device 9 easily rises.
To solve the problem, a solenoid device 9 is proposed in which a plurality of plungers 93 are coupled and integrated, and the integrated plungers 93 are made to reciprocate by using one electromagnetic coil 91 as illustrated in FIG, 30. However, for example, when one of the plurality of contacts 96 adheres, all of the plungers 93 do not reciprocate. As a result, a problem occurs such that the relay 90 cannot be turned off.
The patent literature 2 discloses a solenoid device in which plungers are disposed on the inside of one electromagnetic coil. The solenoid device, however, has a problem such that, since a plurality of plungers are disposed on the inside of the electromagnetic coil, the size of the electromagnetic coil is large. The patent literature 3 discloses a solenoid device in which two plungers are attracted by using two electromagnetic coils. With the configuration, however, the number of electromagnetic coils is large. There is a problem such that the size of the solenoid device cannot be reduced.
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2005-222871
Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2010-212035
Patent Literature 3: Japanese Unexamined Patent Application Publication No. 2010-287455